The invention concerns a vehicle tire and, more particularly, a tire whose architecture is optimized in order to reduce the running noises, while maintaining a high level of performance at the speed limit.
On rolling over roads, vehicle tires produce running noises due, notably, to the contacts of the edges formed by the tread pattern on the road and to the vibrations of compressed air in the grooves of the tire treads, as well as to vibrations of the carcass.
Automobile manufacturers as well as legislators seek to reduce the emission of noise of running vehicles permanently.
What is of interest here is low-speed noise, that is, for example, at a speed less than or equal to 90 km/h.
The contribution of the tire is actually really appreciable only at low speeds. In fact, beyond a certain threshold, noises of the engine, transmission or aerodynamic effects become preponderant.
Numerous efforts have been made to reduce the running noise of tires. For example, one can mention patent U.S. Pat. No. 3,023,798, which proposes modifying the pitch of tread profiles, or patent FR 2,630,374, which proposes imparting to the outer surface of the tire a roughness ranging between 100 and 2000 micrometers.
Furthermore, automobile manufacturers are developing vehicles with ever improved performances, particularly at maximum speed. Thus, customers are demanding silent tires with increased speed resistance at ever lower cost.
The invention concerns a tire whose running noise performances and high running speed resistance are improved.
In the following text, titer means the weight in grams per thousand meters of a reinforcement. The titer is expressed in tex. The stress undergone by a reinforcement or the modulus of that reinforcement is expressed in xe2x80x9ccN/texxe2x80x9d, cN meaning centinewton.
In the following text, xe2x80x9creinforcementxe2x80x9d (xe2x80x9creinforcing threadxe2x80x9d) means any reinforcing element in the form of a thread, capable of reinforcing a given matrix, for example, a tire matrix. One can mention as reinforcements, for example, xe2x80x9cmultifilament yarnsxe2x80x9d, those yarns being twistable or not twistable together, unitary threads such as monofilaments of high elementary diameter, with or without twisting together, wires or xe2x80x9ccordsxe2x80x9d obtained by wiring operations or twisting of those unitary threads or yarns, such reinforcements being possibly hybrid, that is, composite, containing elements of different natures.
xe2x80x9cPlied yarnxe2x80x9d or xe2x80x9cfolded yarnxe2x80x9d means a reinforcement consisting of two fibers (xe2x80x9csingle yarnsxe2x80x9d) or more assembled together by twisting operations; those fibers, generally formed by multifilament yarns, are first individually twisted in one direction (twist direction S or Z) in the course of a first twisting stage, and then twisted together in the opposite direction (twist direction Z or S respectively) in the course of a second twisting stage.
xe2x80x9cAdhesive reinforcementxe2x80x9d means a reinforcement having undergone an appropriate coating treatment, called sizing or adhesion, capable of making that reinforcement adhere, after suitable heat treatment, to the matrix for which it is intended.
The invention concerns a tire containing a crown extended by two sidewalls and two beads, a carcass anchored in both beads, in which the crown contains a reinforcing ply consisting of parallel reinforcements oriented at an angle xcex1 relative to the circumferential direction ranging between 10 and 45 degrees and at least one ply of textile reinforcements circumferentially oriented and spiral-wound. That tire is characterized in that the circumferentially oriented reinforcements possess an initial modulus less than 900 cN/tex and develop a stress under 3% deformation above 12 cN/tex and in that in the tire, when new, the circumferentially oriented reinforcements have, whatever their axial position, a high-temperature contraction potential (CS) less than or equal to the high-temperature contraction potential of the reinforcements before their incorporation in the tire.
It has been found that the use of such a roughly circumferentially oriented reinforcing ply makes it possible to obtain a marked reduction of the running noise of the tire associated with a high level of speed resistance. That reduction can reach 1 dB(A).
The invention also concerns a tire containing a ply of similar spiral-wound circumferentially oriented reinforcements with laying diameters roughly corresponding, over the whole width of the crown, to the final diameters of the reinforcements in the tire after vulcanization.
The circumferentially laid reinforcements, with laying diameters departing, over the whole width of the crown, by at most 0.5% from the final diameters of those reinforcements in the tire after vulcanization, do not undergo any notable shaping operation in the building of the tire or its vulcanization. Such notable shaping would entail, for example, on building or vulcanization, a local extension of those reinforcements exceeding 2 or 3%. That extension generally affects the properties of the reinforcements so deformed, namely, their modulus, their contraction potential and their state of tension. As a result, the reinforcements used in the invention are in a state in the vulcanized tire, over the whole ply, very close to that of the adhesive reinforcement before being placed on the tire. On low-speed rolling, the circumferentially laid reinforcement can support extension in the order of 1 to 2% on passage into the area of contact; thus, the reinforcements used in the invention undergo that type of extension, while behaving like low-modulus reinforcements.
On the other hand, those reinforcements, on high-speed rolling, are stressed to higher deformation and then react as high-modulus reinforcements. They can then ensure effective hooping of the crown, which makes it possible to withstand forces due to centrifugation, even at very high speeds.
The reinforcements of the invention preferably have an initial modulus less than 800 cN/tex and/or develop a stress under 3% deformation above 20 cN/tex.
The mechanical properties of the reinforcements are measured on the reinforcements, which have been subjected to a preconditioning. xe2x80x9cPreconditioningxe2x80x9d is understood to mean the storage of the reinforcements for at least 24 hours, before measurements, in a standard atmosphere according to European Standard DIN EN 20139 (temperature of 20xc2x0xc2x12xc2x0 C.; hydrometry of 65xc2x12%).
Initial modulus means, after having subjected the reinforcements to an initial tension equal to the half-sum of the titers of each of the elementary fibers (i.e., an initial tension of 0.5 cN/tex), the secant modulus measured on the reinforcements, at the same conditions as the preconditioning, under a 0.7% deformation; the samples have an initial length of 400 mm and the rate is 200 mm/min (or 50 mm/minute when their elongation at break does not exceed 5%); the measurements of moduli and stresses are understood to cover the average of ten samples.
Such reinforcements consist of at least one fiber of a material having a high modulus (preferably aramide, but, without departing from the spirit of the invention, it is possible to use other high-modulus textiles originating from liquid crystal polymers like, for example, paraphenylene benzobisoxazole (PBO)) and at least one fiber of a material having a low modulus (preferably nylon, but also polyethylene terephthalate).
The titer of these adhesive reinforcements can range between 250 and 800 tex. The titer is preferably above 400 tex.
The spiral-wound circumferentially oriented reinforcements are preferably arranged in a single layer and the laying pitch of these reinforcements exceeds 1.5 times the diameter of the reinforcements.
According to one advantageous embodiment, the reinforcements of the crown reinforcement ply present an orientation relative to the circumferential direction varying from xcex11 in the midplane of the crown to xcex12 at the lateral ends of said ply with xcex11-xcex12 exceeding 3 degrees. Preferably, xcex11-xcex12 exceeds 8 degrees. The variation of the angle at the edge is made roughly over one-third, if not two-thirds, of the half-width.
The act of increasing the angle of orientation of the reinforcements of the crown reinforcement ply in the center part of the tire increases the running noise gain.
In order to preserve that running noise gain, it has been found that it is desirable to keep xcex11 above 26 degrees and below 38 degrees. Preferably, xcex11 is between 27 and 38 degrees.
The laying pitch of the spiral-wound reinforcement ply can then be less in the lateral zones of the crown that in the center of the tire crown. Lateral zone means from 10 to 35% of the half-width of the crown. Consequently, the hooping density of the circumferentially oriented reinforcements is greater in the lateral zones or shoulders of the tire than in the center. That configuration has the advantage of further improving the running noise gain and of offering an excellent resistance of the shoulder to the centrifugation forces even at the highest speeds. The variation of laying pitch can be greater than or equal to a factor 1.2.
The reinforcing ply roughly spiral-wound circumferentially can be arranged above the reinforcing ply oriented at an angle xcex1. It can also be placed between the carcass ply and the reinforcing ply or even under the carcass ply. Finally, when the crown comprises two reinforcing plies oriented at angles xcex1, xcex2 relative to the circumferential direction, that ply of circumferential reinforcements can be arranged between those two reinforcing plies.
Positioning the reinforcements oriented at 0xc2x0 between or under the angled plies has the effect of increasing, by flattening deflection, the level of deformation imposed on the reinforcements oriented at 0xc2x0. It is then particularly advantageous to use the reinforcements according to the invention in those configurations.
Several embodiments of the invention are now described by reference to the accompanying drawing.